The present invention relates to a tilt damper which securely supports a propelling apparatus externally attached to the stern of a boat at a given angle or provides a supplementary load to the tilting operation of the external propelling device.
The optimum angle for the support of the propelling device externally attached to the stern of a boat varies according to the navigation conditions. It is essential for navigators to securely support the propeller by raising its position so that it can not be subjected to unnecessary shock even when the boat hits submerged obstacles while being towed along the shore. In addition, when towing the boat onshore, it is desirable for the navigator to smoothly tilt the propeller to fully raise it above the water line by inverting its position.
To satisfy these requirements, conventionally, the propeller attached externally to the stern of a boat is supported by a tilt damper. The external propelling device is rotatable and is attached to the stern of the boat by the tilt damper, while the installation angle of the external propelling device is determined by the extended or retracted position of the tilt damper.
One of those conventional tilt damper is specified by the Japanese Patent Publication No. 59-5480 corresponding to the U.S. Pat. Ser. No. No.339,587, which was filed on Mar. 9, 1973, now U.S. Pat. No. 3,863,592.
The above device features the following: Oil and compressed gas are sealed inside the damper cylinder. The piston divides the interior of the damper cylinder into two oil chambers. The orifice and relief valve connecting these oil chambers are provided for the piston in parallel with each other. In response to the internal gas pressure, the piston is subjected to a certain force which causes the piston rod to constantly extend outward in order that the external propelling device can be smoothly rotated against its own weight.
If the external propelling device hits floating obstacles during navigation, the relief valve instantly opens and oil flows from one oil chamber to the other to enable the tilt damper to extend, thus eventually preventing the external propelling device from preventing the external propelling device from incurring external impacts. As soon as the boat is clear from the obstacle, oil is pumped back to the oil chamber through the orifice and the tilt damper can retracts to its original position.
Nevertheless, since the two oil chambers of the tilt damper are continuously interconnected through the orifice to allow the piston to freely reciprocate, a fixed angle cannot optionally be set in the installation of the external propelling device at the stern of the boat. Furthermore, an additional locking mechanism is necessary for securing the external propelling device to the boat at a predetermined angle.
In addition, the locking mechanism was to be used in conjunction with an additional mechanism for the automatic disengagement of the external propelling device to allow the tilt damper to extend as soon as the external propelling device incurs an external impact.
On the other hand, when halting the boat or reversing the rotation of the external propelling device for a reverse course, the damper cylinder is subjected to a tensile force acting in a direction opposite to that generated when the boat moves forward. This leads the damper to extend in the same way as in the case where the boat hits a floating or submerged obstacle. In other words, the conventional tilt damper mechanism cannot securely support the external propelling device when the rotation is reversed.